Conventionally, an unmanned dump truck driving system is well known as a system for transporting earth and sand by a dump truck in a wide range of quarries or the like. The examples of the aforementioned unmanned dump truck driving system are as described below. Teaching a traveling course of an unmanned dump truck has been previously conducted by a specified method, and the coordinate data at each predetermined distance on the traveling course, or at predetermined times, are stored in a storage device. During automatic traveling, the unmanned dump truck confirms the current position at each predetermined sampling time, and the deviation between the actual traveling position and the aforementioned traveling course data, as previously stored, is computed. The steering, vehicle speed, and starting and stopping of the unmanned dump truck are controlled to decrease the deviation, so that the unmanned dump truck is controlled to travel along the traveling course previously stored.
Normally, at specified positions in an unmanned dump truck driving system, a loading site is provided, in an excavating and quarrying site (commonly called a face, and hereinafter referred to as a face), where earth and sand or the like are loaded into the rear deck of the unmanned dump truck, and an earth discharging site (commonly called a hopper, and hereinafter referred to as a hopper) is provided where earth and sand or the like, which have been loaded, are discharged. A plurality of unmanned dump trucks travel between the loading site and the hopper along an automatic traveling course, and repeatedly conduct the operation of discharging the earth and sand or the like, which have been loaded by a loader at the loading site, into the hopper. In such an unmanned dump truck driving system, in many cases, a plurality of unmanned dump trucks are traveling in close proximity to one another in a working area, for example, a loading site, and it is important to prevent collision between these unmanned vehicles.
As a method relating to the prevention of collision, a method for controlling the traveling of an unmanned motor vehicle, such as an unmanned dump truck, is disclosed in, for example, Japanese Laid-open Patent Application No. 5127746. FIG. 5 shows a traveling control method, in a loading area 91 around a face, where a loader (working vehicle) 92 works. The unmanned dump truck 3 has position detecting means (not illustrated) for detecting its current position in a coordinate system on an automatic traveling course 96. The unmanned dump truck 3 travels automatically, with the speed, steering, and the like being controlled by a control means (not illustrated), so as to decrease the deviation obtained by comparing the course data, previously determined by teaching or the like, to the current position detected by the position detecting means. In one embodiment, a plurality of unmanned dump trucks 3, 3a, and 3b are traveling on the same automatic traveling course 96. The unmanned dump truck 3 transmits its current position to other unmanned dump trucks 3a and 3b by means of a transmitter (not illustrated), and receives the current positions of the other unmanned dump trucks 3a and 3b by means of a receiver (not illustrated), so that they recognize the positions of each other.
At the face, the loader 92 loads the unmanned dump truck 3a at a predetermined position. FIG. 5 shows a situation in which the unmanned dump truck 3a stops at a loading position 2. At this point, it is assumed that the other unmanned dump trucks 3 and 3b are approaching the loading position 2, traveling on the automatic traveling course 96a, leading to the face from the hopper. The control means of the unmanned dump truck 3 inputs the current position of the unmanned dump truck 3a by means of the receiver, and when it is determined that the unmanned dump truck 3a is in the loading area 91, the control means halts the unmanned dump truck 3 at a standby point 94 provided just before the entrance of the loading area 91 on the automatic traveling course 96a. When the preceding unmanned dump truck 3a runs along a loading course 96c, leading to the hopper, after completion of loading, and enters the inside of a designated area 95, provided on an automatic traveling course 96d, leading to the hopper, the unmanned dump truck 3, at the standby point 94, starts and travels along an automatic traveling course 96b into the loading area 91.
When the unmanned dump truck 3 at the standby point 94, judges that the preceding unmanned dump truck 3a has left the loading area 91 and is traveling on the automatic traveling course 96d, it starts from the standby point 94 and enters the inside of the loading area 91. Thereafter, the unmanned dump truck 3 reverses from the automatic traveling course 96b and stops at the loading position 2. As described above, interference and collision among the unmanned dump trucks 3, 3a, and 3b, in the loading area 91 are prevented.
Normally, after the loading operation, the loader 92 in the loading area 91 cleans up spilled earth and sand and makes preparations for the next loading at the loading position 2. It the next unmanned dump truck 3 enters the inside of the loading area 91 during the aforementioned operations, there is a danger that an interference or a collision between the unmanned dump truck 3 and the loader 92 may occur.
However, according to the aforementioned conventional method for preventing the entrance into a working area by traveling control, the next unmanned dump truck 3 enters the inside of the loading area 91 even when the loader 92 has not completed the preparations for loading. Accordingly, the operator of the loader 92 has to conduct preparing operation while confirming the position of the unmanned dump truck 3, which is advancing thereto. For this reason, the disadvantages of decreased operation efficiency of the loader 92, increased fatigue of an operator under excessive mental load, and greater risk of interference and collision with the unmanned dump truck 3 arise.